Thanks for coming to Just Answer to ask a question.
1299 means the CHT cylinder head temp sensor has detected an overtemp concern and sent the vehicle into FMEM failure mode effects management. So this means you have a faulty misleading sensor or the vehicle is actually overheating. The sensor is located top front center of the engine.
Here is how to remove it from the end of the cylinder head. The prior view was a 5.4L
I have not heard back from you, so I assume you are needing more assistance on this matter, if so please do reply so I can finish this question. My goal is to have nothing but satisfied customers.
Thanks Hope to hear from you soon, Chris